The common unit of detection in mass spectrometry. Due to the way the magnetic fields work in the mass spectrometer, it's not an ion's mass that's being selected for, but the mass-to-charge ratio which is noted m/z. For many ions, the number of charges carried is simply 1, and the m/z value is effectively the same as the mass of the ion. But for some ions, this is an important distinction that users should be aware of.